Multi-hop communication setup subject to boundary values

ABSTRACT

A method controls the setup of multi-hop communications. For this purpose, boundary values for the multi-hop communications are determined, actual values of the multi-hop communications are detected and multi-hop communications to subscriber terminals are only established if the actual values do not exceed the determined boundary values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/EP2005/051930 filed on Apr. 28, 2005 and GermanPatent Application No. 10 2004 021 319.4 filed Apr. 30, 2004, thecontents of which are hereby incorporated by reference.

BACKGROUND

The present invention relates to a method, a device and a computerprogram for setting up communication links in a radio communicationsystem comprising at least one base station and user terminals, at leastsome of which are implemented as multihop capable ad hoc nodes.

M. Lott et al. “Hierarchical Cellular Multihop Networks”, EPMCC 2003,March 2003 proposes a combination of a cellular mobile communicationsystem, based on an infrastructure of fixed base stations, and aself-organizing WLAN ad hoc mobile communication system. The basestations provide access to a TCP/IP protocol based backbone network. TheWLAN communication system has fixed Internet access points. The range ofcoverage for establishing communication links between an access pointand a WLAN mobile node can be extended by fixed or mobile multihopcapable nodes. The publication explains that a multihop communicationlink requires more network capacity than a direct communication link, ascorresponding transmission resources are required for eachsub-connection making up the complete multihop link.

G. Cristache et al. “Aspects for the integration of ad-hoc and cellularnetworks”, 3rd Scandinavian Workshop on Wireless Ad-hoc Networks,Stockholm, May 6-7 2003 proposes in particular using an ad hoc networkfunction directly for extending the coverage and increasing the cellcapacity of a cellular mobile communication system such as UMTS withoutproviding access points, mobile terminals of the UMTS network beingimplemented in such a way that a communication link is established fromthe base station via a mobile terminal to another mobile terminal.

Coverage extension therefore increases the network radius or rather thecell radius so that even terminals farther from a communication networkor more precisely from a base station can be supplied by said network ormore precisely the relevant base station. However, this has a negativeeffect on the bandwidth of the network as a whole.

SUMMARY

One possible object of the present invention is to provide an improvedway to set up communication links between a base station and userterminals, at least some of which are implemented as multihop capable adhoc nodes.

The inventors propose a method for establishing communication links in aradio communication system having at least one base station and userterminals, at least some of which are implemented as multihop capable adhoc nodes. It is provided that, for at least some of the communicationlinks, limit values for multihop communication links are defined on thepart of the radio communication system, current values for the multihopcommunication links are determined, and multihop communication links touser terminals are then only set up if the limit values defined are notexceeded by the current values. This provides a simple way ofguaranteeing that specifications are met, particularly in respect of therequired bandwidth within the radio communication system. The limitvalues can be defined once or at regular intervals. However, they canalso be dynamically defined and optimized on an event-controlled basis,e.g. if there is a change in the current number of active user terminalsin the particular radio communication system.

It can preferably be provided that individual limit values can be setfor each base station, thereby enabling the limit values to beindividually optimized for each base station depending on the localconditions in the region of the particular base station.

The limit values can basically be defined in any suitable manner and byany suitable entity of the radio communication system. Preferably,however, cell parameters are analyzed by a base station of the radiocommunication system and the limit values for the communication links ofsaid base station are defined on the basis of the result of saidanalysis, thereby enabling the limit values to be defined autonomouslyand individually by each base station.

It can additionally be provided that information about the limit valuesset for the relevant base stations can be exchanged between basestations of the radio communication system, thereby enabling the limitvalues of the base stations to be optimized by mutual coordination amongthe base stations in order to achieve optimum possible network operationalso across base stations. This further development also provides thepossibility of adjusting the limit values of a base station on the basisof the defined limit values of adjacent base stations.

In particular it can be provided that the exchange of information isbased at least in part on an IPv6 protocol. The advantage of protocolsaccording to IPv6 (IP Protocol Version 6) is that even functionalitiesfor communication links from and/or to mobile user terminals areprovided within the framework of said protocols, it being preferablyprovided that the exchange of information is based at least in part on aprotocol according to HMIPv6 (Hierarchical Mobility IPv6). This protocolconstitutes an extension of IPv6 permitting a scalable IP networkinfrastructure including individual mobility anchor points (MAPs),thereby providing particular advantages which also impact precisely thecommunications side of the communication links to user terminals: usingthe MAPs, an IP infrastructure with virtually any hierarchical levelscan be formed, i.e. the IP infrastructure is scalable virtually at willdepending on requirements in terms of network coverage and access nodesto the IP infrastructure. In this way, necessary handovers in particularcan be effected more quickly on the radio network side, as in terms ofsignaling a handover only needs to be handled via the locally affectedMAPs and not, for example, via a single common central device whichwould slow down the handover process.

The limit values can basically be defined on the basis of any suitablespecifications and/or measurement data. However, it is preferablyprovided that the limit values are set on the basis of ad hoc protocoldata. To set the limit values, data present anyway as part of thesetting up or more precisely the signaling of ad hoc communication linksis therefore used, thereby enabling the method to be implemented withminimal additional cost/complexity on the part of the radiocommunication system.

The inventors also propose a device for setting up communication linksin a radio communication system comprising at least one base station anduser terminals, at least some of which are implemented as multihopcapable ad hoc nodes. The device may have the following:

a unit for setting limit values for multihop communication links atleast for some of the communication links,

a unit for comparing the defined limit values with current values forthe multihop communication links, and

a unit for establishing further multihop communication links accordingto the result of the comparison. The advantages resulting from thesetechnical measures have already been explained in analogous manner withreference to the method explained above.

A development of this subject matter features a unit for exchanginglimit value information between base stations of the radio communicationsystem. Once again, for the significance and the advantages of thismeasure, reference is made to the corresponding explanations inconnection with the method described above.

In particular it can be provided that the unit for exchanginginformation is designed at least in part to process an IPv6 protocol, itbeing preferably provided that the unit for exchanging information isdesigned at least in part to process an HMIPv6 protocol. The resultingadvantages specifically for a radio communication system with mobile,multihop capable user terminals have already been explained above withreference to the method.

The inventors further propose a computer program which is preferablydesigned to carry out a method described above. In particular, thecomputer program can be designed to operate in conjunction with thedevice described above.

The computer program may have the following:

a first program routine which calculates and sets limit values formultihop communication links for at least some of the communicationlinks in a radio communication system,

a second program routine for determining current values for the multihopcommunication links and

a third program routine which activates a device for establishingmultihop communication links to user terminals provided that the limitvalues defined are not exceeded by the current values.

The other abovementioned method, data processing and transmission stepsand particularly protocols which are explained in the context of thefollowing descriptions of the figures can basically also be implementedin the form of program routines of this or another suitable computerprogram.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages will become more apparent andmore readily appreciated from the following description of the preferredembodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1: schematically illustrates a hierarchical communicationsinfrastructure

FIG. 2: schematically illustrates an ad hoc coverage extension withoutdefined hop radius

FIG. 3: schematically illustrates an ad hoc coverage extension withdefined hop radii

FIG. 4: schematically illustrates an ad hoc coverage extension withoptimized hop radius

FIG. 5: shows the sequences in the event of a positive comparison resultof the hop radius without communication between the base stations

FIG. 6: shows the sequences in the event of a negative comparison resultof the hop radius without communication between the base stations

FIG. 7: shows the sequences in the event of a positive comparison resultof the hop radius with communication between the base stations

FIG. 8: shows the sequences in the event of a negative comparison resultof the hop radius with communication between the base stations

FIG. 9: shows the protocol stack for connecting mobile IP and ad hoc(AODV)

FIG. 10: schematically illustrates the components of a base stationaccording to one embodiment of the invention

FIG. 11: schematically illustrates a hierarchical communicationsinfrastructure as per FIG. 1, but according to HMIPv6

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments,examples of which are illustrated in the accompanying drawings, whereinlike reference numerals refer to like elements throughout.

The example described below relates to a possibility for setting limitvalues for multihop communication links, wherein a hop radius (maximumpermissible number of hops per communication link) and/or the totalnumber of user terminals in the ad hoc network that are currentlyconnected to a base station are defined. The user terminals of thewireless communication network are able, on the basis of the multihopcapability of at least some of the user terminals, to establish aconnection to the base station via an ad hoc network, even though saiduser terminals are outside the range of the base station. The ad hocnetwork consequently extends the range of the base station by a multihopad hoc routing protocol. This coverage extension is based on the use ofuser terminals in the form of ad hoc nodes acting as routers to provideIP connections which can be used for the communication pathway of therelevant communication link. The wireless communication network can beimplemented e.g. as a suitable UMTS mobile network or even as a WLANnetwork which permits a corresponding ad hoc coverage extension, as isbasically known.

The components and functions of the subject matter will now be brieflyexplained according to the present embodiment:

Base Station:

The base station is the gateway between the ad hoc user terminals and anIP infrastructure (e.g. Internet, see FIGS. 1 and 11). It provides thead hoc user terminals with access to the Internet and therefore allowsad hoc user terminals to be connected to distant communication partnerswhich are likewise connected to an IP-based communicationsinfrastructure. The base station is accordingly designed for connectingad hoc user terminals to the Internet and is therefore designed forprocessing an ad hoc protocol as well as an IP-based mobility protocol.

Hop Radius:

The hop radius corresponds to the maximum permissible hop length fromthe base station to the ad hoc users in the ad hoc network. The hopradius is therefore the maximum permissible number of hops (intermediatenodes) between the base station and an ad hoc user terminal. The numberof hops is communicated to the base station using the ad hoc protocol,or more precisely can be ascertained by the base station from therouting information. For example, if such a connection has three hops,the base station, an ad hoc user terminal and two further ad hoc nodesare contained in said connection. If the maximum permissible hop countis increased, i.e. the hop radius is extended, the network loadincreases, as even more ad hoc users may therefore be included in the adhoc network around the base station. A hop radius can be set by the basestation itself. On the basis of the radius defined, ad hoc userterminals whose hop length would exceed the hop radius are not acceptedinto the ad hoc network around the corresponding base station, whichmeans that the network and the network load remain stable.

Ad Hoc User Count:

Alternatively or additionally to the abovementioned method, the absolutenumber of ad hoc user terminals within an ad hoc network can be takeninto account for calculating the network load and setting the hopradius. As an alternative to setting a hop radius as the limit value, amaximum number of ad hoc user terminals can also be defined as the limitvalue within an ad hoc network, it being possible to stipulate, forexample, that the hop radius for a particular base station shall not bereduced as long as a particular number of ad hoc user terminals is notexceeded.

A trade-off between hop radius and maximum permissible ad hoc user countcan also be implemented (hybrid method):

The abovementioned methods for setting the hop radius and the maximumpermissible number of ad hoc user terminals can be combined foroptimized calculation of the network load, a trade-off being possiblewhich allows improved network planning as a trade-off between a hopradius algorithm and ad hoc user count algorithm. Correspondingassessment parameters are preferably calculated here on the basis ofsaid algorithms. This calculation can be performed autonomously by thebase station and used for setting both the hop radius and the maximumpermissible number of ad hoc users. A virtual coverage radius canpreferably also be defined as a further limit value for this method.Said virtual coverage radius constitutes a value which is determined asa function of the defined and/or determined values for the hop radiusand the maximum permissible number of ad hoc users. The greater the hopradius and the higher the ad hoc user count, the greater the coverageradius also. In the simplest case, the coverage radius is directlyproportional to the hop radius and to the ad hoc user count.

Communication Between the Base Stations:

A specific communication protocol is used for data exchange betweendifferent base stations FA-BS1 to FA-BS4 (see FIG. 1). Saidcommunication protocol provides for the exchange of limit valueinformation, such as the hop radius or the maximum permissible number ofad hoc users, between (preferably adjacent) base stations FA-BS1 toFA-BS4. The information can be exchanged e.g. via an IP infrastructureschematically illustrated in FIG. 1 to which the base stations FA-BS1 toFA-BS4 are connected. For this purpose a hierarchical mobile IPinfrastructure can be provided which allows higher-order entities(mobility agents) to coordinate the exchange of information between thebase stations FA-BS1 to FA-BS4. In the example shown in FIG. 1 these areimplemented as regional foreign agent RFA and/or gateway foreign agentGFA. FIG. 11 shows an alternative embodiment based on IPv6. The IPstructure according to HMIPv6 is illustrated, only mobility anchorpoints (MAP) that are in principle functionally equivalent beingprovided instead of the strictly defined RFA and GFA. The base stationsBS1 to BS4 are used as access routers AR, which means that the IPinfrastructure is scalable virtually as required. This will be explainedin greater detail below.

The mobility agents RFA, GFA as shown in FIG. 1 are connected to thebase stations FA-BS1 to FA-BS4 at data link level, making it easy fordata to be exchanged between the different base stations FA-BS1 toFA-BS4. The abovementioned protocol permits this data exchange as partof the autonomous adaptation and optimization of network planning, basedon the hop radius and/or the maximum permissible ad hoc user count.

With the method, limit values are set for an ad hoc network around abase station, thereby also finally setting the extent of the coverageextension around the corresponding base station. In general, smaller hopradii or lower ad hoc user counts necessarily also result in a smallerenlargement of the coverage extension attained by the ad hoc networkaround a corresponding base station. This fact can be taken into accountin the context of defining the abovementioned virtual coverage radius.

The setting of limit values is necessary in order to prevent long IProutes being set up by far distant ad hoc user terminals MN0, MN1 over alarge number of hops which would in turn reduce the bandwidth of theoverall ad hoc network around a base station FA-BS1 to FA-BS4. This willnow be illustrated even more clearly with reference to FIGS. 2 to 4. Bysetting limit values, a base station FA-BS1 to FA-BS4 can thereforeultimately be influenced as to whether a distant user terminal MN0, MN1is to be accepted into its own ad hoc network. This requires analgorithm which defines a criterion from the existing number of ad hocusers and the hop lengths so that the bandwidth can be maintained.

Moreover, each base station FA-BS1 to FA-BS4 can decide, on the basis ofthe limit values set and the exchange of information with other basestations FA-BS1 to FA-BS4 and/or with a particular ad hoc user terminalMN0, whether said ad hoc user terminal MN0 is to be accepted into itsown ad hoc network, particularly if said ad hoc user terminal MN0 cannotdetermine for itself any other possible connection to other basestations FA-BS1 to FA-BS4. In this case the user terminal MN0 can send acorresponding request to the only reachable base station FA-BS1 toFA-BS4. This is particularly the case when only one base station FA-BS1is present, or the base stations FA-BS2 to FA-BS4 adjacent to a firstbase station FA-BS1 are so defined that they cannot change the hopradius set for them such that said user terminal MN0 can be acceptedinto their ad hoc network.

As already explained, it is preferably provided that the base stationsFA-BS1 to FA-BS4 exchange the information concerning a provisionally sethop radius among one another. This information exchange can take placeas broadcast/multicast and can consequently use the existing IP-basedinfrastructure shown in FIG. 1. On the basis of the received informationof adjacent base stations FA-BS1 to FA-BS4, each of the base stationsFA-BS1 to FA-BS4 can vary the provisional hop radius in one or moreiterative optimization steps such that as large a plurality of ad hocuser terminals MN0, MN1 as possible can be supplied, where necessarytaking minimum values for the bandwidth of each of the ad hoc networksinto account. This optimization can also be carried out dynamically,e.g. in the event that the network load of a particular base stationFA-BS1 increases and the hop radius of said base station FA-BS1 musttherefore be reduced. As part of said optimization process it can bedetermined whether and to what extent other base stations FA-BS2 toFA-BS4 can extend their respective hop radius, thereby allowingarea-wide data supply of the ad hoc user terminals MN0, MN1 so that eachad hoc user terminal MN0, MN1 can establish a data connection to a basestation FA-BS1 to FA-BS4. This will be explained more clearly below withreference to FIGS. 3 and 4.

In addition, within the ad hoc protocol, signaling can be providedbetween base stations FA-BS1 to FA-BS4 and ad hoc user terminals MN0,MN1 and likewise further signaling can be provided within the IPprotocol between different, preferably adjacent base stations FA-BS1 toFA-BS4, permitting a particular base station FA-BS1 to reject, oranother base station FA-BS2 to FA-BS4 to assign, an additional ad hocuser terminal MN1.

As already explained, each ad hoc user terminal MN0, MN1 wishing tocommunicate with the Internet requires a base station FA-BS1 to FA-BS4as a default gateway so that the routing requests are forwarded to theInternet. For this purpose an IP-based mobility protocol is used whichcan forward the requests and responses to the relevant base stationFA-BS1 to FA-BS4. In addition, by using a mobility protocol of this kind(e.g. mobile IP/HMIP/FMIP), the global mobility of any ad hoc userterminal MN0, MN1 can be supported. This allows roaming between disjointad hoc networks of different base stations FA-BS1 to FA-BS4 and alsobetween different IP infrastructures at any time, without disturbingexisting IP connections.

A plurality of base stations may be disposed in a distributed manner, itbeing possible to increase the coverage of the base stations by usingmultihop capable terminals and ad hoc routing protocols, whereby therange of the base station (coverage extension radius) generally expandswith the number of connected ad hoc nodes. Measurements show that thisexpansion has a negative effect on data throughput. By limiting the hoplength, i.e. defining the hop radius and/or limiting the number ofpermissible ad hoc nodes, the network load can be optimized. The datarate and network load can be independently controlled on the part of thebase stations in such a way that the actual network load does not exceeda predefined maximum network load, thereby enabling the required datarate to be maintained for each ad hoc user terminal for ad hoc dataconnections via the respective base station.

According to the related art, an ad hoc multihop protocol currentlymakes no provision for a maximum permissible hop length or moreprecisely a defined hop radius for connecting ad hoc user terminals toexisting ad hoc networks. Rather, according to the related art it isgenerally the case that all users are accepted into an existing hocnetwork, irrespective of the number of hops. Moreover, no autonomousagreement among the base stations concerning limit values and wherenecessary their optimization is currently provided in the protocolsaccording to the related art.

The above described method will now be explained in detail.

1. Method for determining the hop length and setting the hop radius:

a) Definition of an optimum network load by the base station b)Determination of the actual network load by the base station

c) Comparison of the optimum network load with the maximum permissiblenetwork load by the base station

d) Setting of a hop radius on the basis of the results from step c)

e) Transmission of information concerning the hop radius set to adjacentbase stations via the abovementioned protocol

f) Autonomous adjustment of the hop radius by the base station on thebasis of information received concerning the hop radii of adjacent basestations

2. Method for determining the maximum number of ad hoc users (nodecount):

a) Definition of an optimum node count by the base station

b) Determination of the actual node count by the base station

c) Comparison of the optimum node count with the maximum permissiblenode count by the base station

d) Setting of a maximum permissible node count

e) Transmission of information concerning the node count set to adjacentbase stations via the abovementioned protocol

f) Autonomous adjustment of the node count by the base station on thebasis of information received concerning the node count of adjacent basestations

3. Method for the combined setting of the hop length and ad hoc usercount (hybrid method):

a) Defining of the optimum network load, relating to an optimum ad hocnode count and hop radius, by the base station

b) Determination by the base station of the actual network load,relating to the actual number of ad hoc nodes and the actual hop radius

c) Comparison of the actual network load with the optimum network loadby the base station

d) Setting of the hop radius and maximum permissible node count

e) Transmission of information concerning the hop radius and node countset to adjacent base stations via the abovementioned protocol

f) Autonomous adjustment of the hop radius and node count by the basestation on the basis of information received concerning the hop radiusand node count of adjacent base stations

A possible implementation of the method for determining the hop radiuswill now be described by way of example:

An algorithm is used which evaluates the load and status of a basestation in conjunction with the connected ad hoc network. Thisevaluation forms the basis for determining the hop density and hoplength. The density is calculated from the number of ad hoc userterminals divided by the hop radius. Individual results from the ad hocdensity calculation which are determined at different points in time canalso be averaged and used for a comparison. If the hop count increases,an increasing network density must also be assumed. An increase in thenetwork density will in turn increase the network load. This in turnresults in the minimizing of the data rate of all the ad hoc userterminals. To ensure that the base station can maintain the determineddata rate for all the ad hoc user terminals, the network must belimited. This can be determined by active measurement or by comparisonvalues, thereby enabling the optimum network density to be defined. Thevalues required for this purpose are known to the relevant base station.

When an ad hoc network is set up, the base station can compare thecurrent network density, obtained on the basis of the currentlydetermined number of ad hoc user terminals, with stored and/or averagedsetpoint values and define the hop radius autonomously. By theindependent comparison on the part of the base station between thesetpoint value of the network density and the actual value of thedensity of the ad hoc nodes present, the base station can determine thehop radius and use it to decide whether a new ad hoc user terminal is tobe admitted. Ad hoc user terminals with a hop length that is less thanor equal to the hop radius can be accepted into the ad hoc network bythe base station. However, this increases the network load. Anyexceeding of the setpoint value or maximum value of the network load canbe prevented by the above described comparison of the current ad hocuser count with the defined maximum permissible number of ad hoc userterminals and, where necessary, by rejecting the new user terminal, orby re-calculating the current network load and if necessary reducing thehop radius.

The criterion for an ad hoc node, to set up a route to a particulardestination node, currently depends on a hop metric which is based onselecting the shortest path and using it as the communication path.Consequently an ad hoc node will generally opt for a base stationproviding the shortest path. However, this is impermissible if theselected path length exceeds the hop radius of the ad hoc network of thecorresponding base station.

FIG. 1 schematically illustrates the layout of a hierarchicalcommunications infrastructure. Four base stations FA-BS1 to FA-BS4 areshown by way of example in FIG. 1. According to the IP protocolrepresented in FIG. 1, these four base stations FA-BS1 to FA-BS4 areimplemented as foreign agents which are interconnected at leastregionally via regional foreign agents RFA. In the case of IPv6, asshown in FIG. 11, this layout corresponds to a structure comprisingmobility anchor points (MAP) which perform local registration of the adhoc user terminals. FIG. 1 additionally shows two mobile ad hoc nodesMN0, MN1 which move freely between the four base stations FA-BS1 toFA-BS4.

FIG. 2 shows an ad hoc network structure comprising four ad hoc networkseach having ad hoc user terminals A and a base station B. No limit valuehas been defined for the hop length between the base stations B and thead hoc user terminals A. This results in an undefined network structurearound each of the base stations B and an asymmetrical network loaddistribution among or around the individual base stations B which takesabsolutely no account of the maximum data transmission capacity of thebase stations B.

FIG. 3 shows a situation according to FIG. 2 but in which in order toimplement the ad hoc coverage for each base station B a defined hopradius, i.e. a maximum permissible number of hops (hop=1, 1, 2, 3), hasbeen set. By determining the network load and taking into account thecapability or more specifically the transmission capacity of theparticular base station (i.e. the maximum theoretically possible networkload, the capacity of the connection to the IP backbone also beingcritical here), an individually optimum hop radius can be set by eachbase station. However, FIG. 3 shows that if only a hop radiusindividually set by a base station B is set, the situation may arisethat particular ad hoc user terminals are not supplied by a base stationB.

FIG. 4 shows the situation according to FIG. 3 after the individuallyset hop radius of the base stations B has been further optimizedregionally and/or globally in one or more iterative optimization stepsby an agreement between the base stations B such that all the ad hocuser terminals A can be supplied, resulting in hop radii (hop=1, 2, 2,3). A dynamic network load distribution is also possible here which,while allowing preferably each base station B to manage only as many adhoc user terminals as it can accommodate on the basis of its owncapability, nevertheless allows all the user terminals A to be supplied.This means that any increase in network load above the capacity of eachbase station B can be avoided while nevertheless ensuring area-widecoverage.

FIG. 5 shows the sequences of the proposed protocol when the userterminal MN(n) attempts to take up a connection to the base stationBS(n) in order to obtain access to the Internet via said base station asthe default gateway. For this purpose MN(n) sends a base station requestBS Req via a multihop capable terminal MN(n+1) which is already part ofthe ad hoc network of the base station BS(n), whereupon BS(n) comparesthe hop length with the defined hop radius. As this is met, BS(n)accepts the user terminal MN(n). The latter then initiates theregistration process with the home agent (HA) or with the correspondentnode (CN) and sends a binding update BU. This is confirmed by the homeagent (BU ACK). At this point in time the connection is completelyestablished. User terminal MN(n) is now connected to an IP-basedinfrastructure (e.g. the Internet).

Analogously to FIG. 5, FIG. 6 shows the sequences of the proposedprotocol when the user terminal MN(n) attempts to take up a connectionto the base station BS(n) in order to obtain access to the Internet viasaid base station as the default gateway. For this purpose MN(n) sends abase station request BS Req via a multihop capable terminal MN(n+1)which is already part of the ad hoc network of the base station BS(n),whereupon BS(n) compares the hop length with the defined hop radius. Asa result, however, the base station BS(n) in this case ascertains thatthis is not met. BS(n) therefore sends a negative acknowledgement BSNACK.

User terminal MN(n) now starts with a new base station request BS Req.Another base station BS(n+1) then answers. The latter could also havealready responded to the first request. However, the user terminal MN(n)has no knowledge as to which BS is able to accept it. The first BS willnot therefore reply to the second request (storing of the request canpreferably be provided). After comparison of the hop length with the hopradius, BS(n+1) is ready to accept the new node MN(n), and sends apositive acknowledgement BS ACK.

Thereafter user terminal MN(n) begins sending the binding update (BU) tothe home agent (HA). The connection is completely established.

FIG. 7 shows the sequences when the user terminal MN(n) attempts to logonto base station BS(n). For this purpose MN(n) again sends a requestvia a multihop capable terminal MN(n+1) which is already part of the adhoc network of the base station BS(n). The base station BS(n) comparesthe hop length with a defined hop radius. The result of the comparisonis that the user MN(n) would have to be rejected. Before the basestation BS(n) rejects the new user MN(n), the base station BS(n) beginsinterrogating adjacent base stations BS(n+1) in order to ascertain theirhop radius. For this purpose BS(n) sends a HOP request (HOP Req). Thereply of the adjacent base station BS(n+1) produces the result thatBS(n) must nevertheless accept the new user MN(n). The connection is thecompletely established. This may be due to the fact that the otherBS(n+1) has reached its capacity limit, which may be indicated by a lowhop radius. BS(n) possesses the highest hop radius and can increase itso that the new user terminal MN(n) can be accepted. Should BS(n) not beable to increase the hop radius, as the capacity limit has been reached,the new user terminal MN(n) will not be accepted. The latter can or mustnow change, for example, to a higher-order network, e.g. a cellularmobile network, by a vertical handoff.

FIG. 8 shows the sequences for the attempt of the user terminals MN(n)to log onto the base station BS(n) via a multihop capable terminalMN(n+1). The base station BS(n) compares the hop length with a definedhop radius. The result of the comparison is that the user MN(n) wouldhave to be rejected. Before the base station BS(n) rejects the new userMN(n), the base station BS(n) begins to interrogate the adjacent basestation BS(n+1) in order to ascertain its hop radius. For this purposeBS(n) sends a HOP request HOP Req. The reply of the adjacent basestation BS(n+1) produces the result that BS(n) does not need to acceptthe new user MN(n). BS(s) therefore sends a BS NACK, whereupon MN(n)sends a BS Req in order to seek out another base station. BS(n+1), whichposses a higher hop radius, responds. Said base station BS(n+1) comparesthe request with its hop radius and accepts the new user MN(n). Thelatter then sends the binding update (BU) to the home agent (HA). Theconnection is completely established.

FIG. 9 shows the protocol stack for the integration of mobile IP andAODV (ad hoc on-demand distance vector routing protocol) which has beenused for the protocol described here by way of example. The followingmobility agents are shown: correspondent node (CN), home agent (HA),gateway foreign agent (GFA), regional foreign agent (RFA) and foreignagent (FA). In addition, the connection of an ad hoc network comprisingMN(n) and MN(n+1) is shown.

The ad hoc routing protocol (here AODV) is used for the connection andtransmission of IP routing packets. The HMIP protocol stack is used forconnecting mobile user terminals to the Internet when these changebetween the IP networks. For this purpose the ad hoc user terminals sendthe binding update (BU) via the base station, said base station beingthe FA constituting the gateway between the ad hoc network and the IPinfrastructure.

The protocol is implemented for HMIPv6, only mobility anchor points MAPaccording to FIG. 11 are provided instead of gateway foreign agent (GFA)and regional foreign agent (RFA).

FIG. 10 schematically illustrates the components of a base station BS1for establishing communication links in a radio communication systemcomprising at least a plurality of base stations BS1, BS2 and userterminals MN0, MN1. The user terminals MN0, MN1 are implemented asmultihop capable ad hoc nodes. The user terminal MN0 attempts toestablish an ad hoc communication link to the base station BS1 via theuser terminal MN1.

The base station BS1 has a limit value definition unit LVDU for definingthe hop radius for multihop communication links. Said LVDU is connectedat data link level to a limit value comparison unit LVCU for comparingthe defined hop radius with current values for the hop length of thecommunication link currently in question. Said LVCU is in turn connectedat data link level to a multihop communication unit MHCU forestablishing further multihop communication links depending on theresult of the comparison. Finally, at least the LVDU is connected atdata link level to an information exchange unit IXU for exchanging hopradius information between base station BS1 and one or more adjacentbase stations BS2 of the radio communication system.

Analogously to FIG. 1, FIG. 11 shows a structure for implementing HMIPv6within the framework of the method, wherein instead of the gatewayforeign agent GFA and the regional foreign agents RFA only mobilityanchor points MAP are provided which can basically be disposed in anyhierarchical levels. The base stations BS1 to BS4 are used in this caseas access routers AR. An IP infrastructure of this kind is scalable asrequired, i.e. basically any number of MAPs can be provided in anyhierarchical arrangement in order to provide a desired network coverageor more precisely a desired number of network accesses. The networkhierarchy can also be implemented differently in different branches ofthe IP infrastructure, as schematically illustrated in FIG. 11 for theleft- and right-hand branch of the IP infrastructure. This shows thatfor a user terminal MN1 a handover, for example, from the base stationBS3 to the base station BS4 can generally be handled faster, as onlylocal MAPs need to be involved at signaling level in the handover andnot a central device such as an RFA or GFA.

A description has been provided with particular reference to preferredembodiments thereof and examples, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the claims which may include the phrase “at least one of A, B and C”as an alternative expression that means one or more of A, B and C may beused, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69USPQ2d 1865 (Fed. Cir. 2004).

The invention claimed is:
 1. A method for controlling whether toestablish multi-hop communication links in a radio communication systemcomprising a plurality of base stations and a plurality of userterminals, at least some of which are implemented as multi-hop-capablead hoc nodes, comprising: establishing a limit value for each basestation for multi-hop communication links between the base station anduser terminals; comparing the limit value with a corresponding currentvalue for multi-hop communication links, the limit value being comparedat the base station; determining at the base station whether toestablish a new multi-hop communication link between the base stationand a user terminal, based on whether the limit value is exceeded by thecurrent value; establishing the new multi-hop communication link betweenthe base station and the user terminal only if the limit value is notexceeded by the current value; and exchanging information concerninglimit values between base stations of the radio communication system. 2.The method as claimed in claim 1, wherein each limit value relates to amaximum number of hops allowed for the new multi-hop communication linkor a maximum number of multi-hop communication connections that will behandled by the base station.
 3. The method as claimed in claim 1,wherein each limit value is set individually for the base station. 4.The method as claimed in claim 1, wherein each base station defines acell, for at least one of the base stations, cell parameters areanalyzed by the base station to produce a result, and each base stationsets its respective limit value based on the respective result.
 5. Themethod as claimed in claim 1, wherein the information concerning limitvalues is exchanged based at least in part on an IPv6 protocol.
 6. Themethod as claimed in claim 5, wherein the information concerning limitvalues is exchanged based at least in part on an HMIPv6 protocol.
 7. Themethod as claimed in claim 1, wherein the limit value of each basestation is adjusted based on limit values of adjacent base stations. 8.The method as claimed in claim 1, wherein the limit values are definedbased on ad hoc protocol data.
 9. A device for controlling whether toestablish multi-hop communication links to/from user terminals in aradio communication system, at least some of the user terminals beingimplemented as multi-hop capable ad hoc nodes, comprising: a unit fordefining a limit value for multi-hop communication links between a basestation and user terminals; a unit provided in the base station forcomparing the limit value with a current value for multi-hopcommunication links and producing a result; a unit provided in the basestation for determining whether to set up a further multi-hopcommunication link between the base station and a user terminal, basedon the result; and a unit provided in the base station for exchanginglimit value information with other devices of the radio communicationsystem.
 10. The device as claimed in claim 9, wherein the unit forexchanging limit value information operates based on an IPv6 protocol.11. The device as claimed in claim 9, wherein the unit for exchanginglimit value information operates based on an HMIPv6 protocol.
 12. Anon-transitory computer readable medium storing a computer program forcausing a computer to execute a method for controlling whether toestablish multi-hop communication links in a radio communication systemhaving ad hoc network capability, the computer program comprising: afirst program routine which calculates and defines a limit for value formulti-hop communication links between a base station and user terminals;a second program routine for determining a current value for multi-hopcommunication links; a third program routine executed in the basestation for determining whether to establish a new multi-hopcommunication link from the base station to a user terminal based onwhether the limit value is exceeded by the current value; a fourthprogram routine which activates a device for setting up a multi-hopcommunication link to the user terminal only if the limit value is notexceeded by the current value; and a fifth program routine to exchangethe limit value with another base station.
 13. A method for controllingwhether to establish multi-hop communication links in a radiocommunication system comprising a plurality of base stations and aplurality of user terminals, at least some of which are implemented asmulti-hop-capable ad hoc nodes, comprising: establishing a limit valuefor each base station for multi-hop communication links between the basestation and user terminals; comparing the limit value with a proposedvalue that will result if a proposed multi-hop communication link isestablished, the limit value being compared at the base station;determining at the base station whether to establish the proposedmulti-hop communication link as a new multi-hop communication link fromthe base station to a user terminal, based on whether the limit value isexceeded by the proposed value; establishing the new multi-hopcommunication link from the base station to the user terminal only ifthe limit value is not exceeded by the proposed value; exchanginginformation concerning limit values between base stations of the radiocommunication system; and independently varying the limit values betweenthe base stations to adjust each base station's coverage area andoptimize network utilization.
 14. The method as claimed in claim 13,wherein each base station is associated with a cell, increasing thelimit value increases a size of the cell, and decreasing the limit valuedecreases the size of the cell.